1. Field of the Invention
The present invention relates to tissue interface devices, and more particularly to a tissue interface device wherein fluid is extracted from a biological tissue and placed into contact with a sensor for sensing a characteristic of the fluid flowing from an artificial opening in a biological membrane.
2. Background Art
Monitoring systems that sample and measure characteristics of fluids from a biological tissue, such as on a human, are well known. Many of these systems involve implanting sensors and related devices into the organism (such as under the skin) in order to obtain fluid samples and make measurements of those samples. Implanted sensors, in addition to the pain caused to the organism during the implantation of the sensor, degrade rapidly when introduced into the organism. Even for short term implants, it has been shown that within the first several hours after implantation a rapid deposition of fibroblasts, macrophage plaques, fibrogen growth and other natural physiological encapsulation processes surround the implant and thereby impair, restrict, and modify, in a dynamic fashion, the free flow of the analytes of interest into the active sensor region of the implanted device.
Alternatively, fluids may be drawn from the biological membrane of the organism through the use of needle or cannula that penetrate deep into the membrane (such as penetrating deep into the dermis or subcutaneous tissue of a human). The extracted fluid is drawn toward a remote sensor or sensor array for measurement of the desired characteristic. This solution requires a large volume of fluid be drawn before the fluid reaches the sensor. Further, this solution can have detrimental effects on the measurement of a desired current analyte concentration level because of the lag time imposed by the large inherent time delay required for the fluid to reach the sensor from the point of fluid withdrawal. Because of the lag time, approximation techniques must be applied to provide a more time-accurate indication of the current concentration of the desired analyte in the fluid.